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Journal Articles

Simulation study on the design of nondestructive measurement system using fast neutron direct interrogation method to nuclear materials in fuel debris

Maeda, Makoto; Furutaka, Kazuyoshi; Kureta, Masatoshi; Ozu, Akira; Komeda, Masao; Toh, Yosuke

Journal of Nuclear Science and Technology, 56(7), p.617 - 628, 2019/07

Journal Articles

Measurement of neutron scattering cross section of nano-diamond with particle diameter of approximately 5 nm in energy range of 0.2 meV to 100 meV

Teshigawara, Makoto; Tsuchikawa, Yusuke*; Ichikawa, Go*; Takata, Shinichi; Mishima, Kenji*; Harada, Masahide; Oi, Motoki; Kawamura, Yukihiko*; Kai, Tetsuya; Kawamura, Seiko; et al.

Nuclear Instruments and Methods in Physics Research A, 929, p.113 - 120, 2019/06

A nano-diamond is an attractive neutron reflection material below cold neutron energy. The total neutron cross section of a nano-diamond was derived from a neutron transmission measurement over the neutron energy range of 0.2 meV to 100 meV because total neutron cross section data were not available. The total cross section of a nano-diamond with particle size of approximately 5 nm increased with a decrease in neutron energy to 0.2 meV. It was approximately two orders of magnitude larger than that of graphite at 0.2 meV. The contribution of inelastic scattering to the total cross section was to be shown negligible small at neutron energies of 1.2, 1.5, 1.9, 2.6, and 5.9 meV in the inelastic neutron scattering measurement. Moreover, small-angle neutron scattering measurements of the nano-diamond showed a large scattering cross section in the forward direction for low neutron energies.

JAEA Reports

Technical design of the pressure-resistant chamber for open inspections of the storage containers of nuclear fuel materials

Marufuji, Takato; Sato, Takumi; Ito, Hideaki; Suzuki, Hisashi; Fujishima, Tadatsune; Nakano, Tomoyuki

JAEA-Technology 2019-006, 22 Pages, 2019/05

JAEA-Technology-2019-006.pdf:2.84MB

Radioactive contamination incident occurred at Plutonium Fuel Research Facility (PFRF) in Oarai Research and Development Institute, Japan Atomic Energy Agency on June 6, 2017. During inspection work of storage container containing nuclear fuel materials, the PVC bag packaging in the storage container ruptured when a worker opened the lid in the hood, and a part of contents was spattered over the room. The cause of the increase of internal pressure of the storage container was gas generation by alpha radiolysis of the epoxy resin mixed with nuclear fuel materials. Opening inspection of about 70 similar containers stored in PFRF has been planned to confirm the condition of the contents and to stabilize the stored materials containing organic compounds. For safe and reliable open inspection of the storage containers with high internal pressure in the glove box, it is necessary to develop a pressure-resistant chamber in which the storage containers are opened and the contents are inspected under gastight condition. This report summarizes the concerns and countermeasures of the chamber design and the design results of the chamber.

Journal Articles

A Conceptual design study of pool-type sodium-cooled fast reactor with enhanced anti-seismic capability

Kubo, Shigenobu; Chikazawa, Yoshitaka; Ohshima, Hiroyuki; Uchida, Masato*; Miyagawa, Takayuki*; Eto, Masao*; Suzuno, Tetsuji*; Matoba, Ichiyo*; Endo, Junji*; Watanabe, Osamu*; et al.

Proceedings of 27th International Conference on Nuclear Engineering (ICONE-27) (Internet), 8 Pages, 2019/05

The authors are developing the design concept of pool-type sodium-cooled fast reactor (SFR) that addresses Japan's specific siting conditions such as earthquakes and meets safety design criteria (SDC) and safety design guidelines (SDGs) for Generation IV SFRs. The development of this concept will broaden not only options for reactor types in Japan but also the range and depth of international cooperation. A design concept of 1,500 MWt (650 MWe) class pool-type SFR was thought up by applying design technology obtained from the design of advanced loop-type SFR, named JSFR, equipped with safety measures that reflect results from the feasibility study on commercialized fast reactor cycle systems and fast reactor cycle technology development, improved maintainability and repairability, and lessons learned from the Fukushima Daiichi Nuclear Power Plants accident.

Journal Articles

Estimation method of systematic uncertainties in Monte Carlo particle transport simulation based on analysis of variance

Hashimoto, Shintaro; Sato, Tatsuhiko

Journal of Nuclear Science and Technology, 56(4), p.345 - 354, 2019/04

 Percentile:100(Nuclear Science & Technology)

Particle transport simulations based on the Monte Carlo method have been applied to shielding calculations. Estimation of not only statistical uncertainty related to the number of trials but also systematic one induced by unclear physical quantities is required to confirm the reliability of calculated results. In this study, we applied a method based on analysis of variance to shielding calculations. We proposed random- and three-condition methods. The first one determines randomly the value of the unclear quantity, while the second one uses only three values: the default value, upper and lower limits. The systematic uncertainty can be estimated adequately by the random-condition method, though it needs the large computational cost. The three-condition method can provide almost the same estimate as the random-condition method when the effect of the variation is monotonic. We found criterion to confirm convergence of the systematic uncertainty as the number of trials increases.

JAEA Reports

Restoration activity of the contamination accident at plutonium fuel research facility

Restoration Activity Team for the PFRF Contamination Incident

JAEA-Review 2019-001, 58 Pages, 2019/03

JAEA-Review-2019-001.pdf:10.74MB

The contamination accident occurred in a laboratory room (Room No.108) of Plutonium Fuel Research Facility (PFRF) in Japan Atomic Energy Agency (JAEA), Oarai Research and Development Institute on June 6, 2017. The polyvinyl chloride (PVC) bags burst just after the lid of one storage container was opened during the inspection of storage containers for U and Pu in the ventilation hood. At that time, part of nuclear materials in the storage container were scattered all over the room. Five workers in the room were subjected to plutonium contamination, which resulted in internal exposure. In order to restore the Room No.108 of PFRF, the Restoration Activity Team organized in JAEA carried out the decontamination work after the investigation of the contamination level in the room. The team decontaminated the surface of walls, ceiling, gloveboxes and other experimental instruments. Depending on the contamination distribution and installation state of the instruments, suitable decontamination methods were selected. In addition to the manual wiping using wet clothes, the exfoliation method using a strippable paint was applied for constricted areas. As a result, the loose alpha-contamination level fell below the detection limit throughout the room. On the other hand, the fixed contamination was covered with plastic sheets after the decontamination by a strippable paint. We hope that the restoration activity described in this report will provide useful information for the management of decommissioning facilities, especially for facilities treating alpha-radioactive materials such as plutonium.

JAEA Reports

Progress report on Nuclear Safety Research Center; JFY 2015 - 2017

Nuclear Safety Research Center, Sector of Nuclear Safety Research and Emergency Preparedness

JAEA-Review 2018-022, 201 Pages, 2019/01

JAEA-Review-2018-022.pdf:20.61MB

Nuclear Safety Research Center (NSRC), Sector of Nuclear Safety Research and Emergency Preparedness, Japan Atomic Energy Agency (JAEA) is conducting technical support to nuclear safety regulation and safety research based on the Mid-Long Term Target determined by Japanese government. This report summarizes the research structure of NSRC and the cooperative research activities with domestic and international organizations as well as the nuclear safety research activities and results in the period from JFY 2015 to 2017 on the nine research fields in NSRC; (1) severe accident analysis, (2) radiation risk analysis, (3) safety of nuclear fuels in light water reactors (LWRs), (4) thermohydraulic behavior under severe accident in LWRs, (5) materials degradation and structural integrity, (6) safety of nuclear fuel cycle facilities, (7) safety management on criticality, (8) safety of radioactive waste management, and (9) nuclear safeguards.

Journal Articles

Comparison of airborne and ground-based tools used for radiation measurement in the environment

Ochi, Kotaro; Sasaki, Miyuki; Ishida, Mutsushi*; Sanada, Yukihisa

Progress in Nuclear Science and Technology (Internet), 6, p.103 - 107, 2019/01

After the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, a large amount of radionuclides was spread out all over the world. In our previous study, we developed the aerial radiation monitoring technique using unmanned helicopter for investigating the dose rate derived deposited radionuclides over wide area. In addition, many monitoring techniques were developed for investigating the local distribution of radionuclides using unmanned aerial vehicle, handheld instrument and car within small area. Distinction of these methods depends on desirable position resolution of dose rate. However, the comparison method of the measurement result between different methods is not established. In this study, we attempted to evaluate the some methods of airborne and ground radiation measurement in same extended farm.

Journal Articles

Study on restricted use of contaminated rubble on Fukushima Daiichi NPS site, 2; Validation of reference radiocesium concentration for recycling materials

Miwa, Kazuji; Shimada, Taro; Takeda, Seiji

Progress in Nuclear Science and Technology (Internet), 6, p.166 - 170, 2019/01

In this study, in order to validate the restricted use of recycling material at the reference radiocesium concentration (determined in series report (1)), we evaluated worker annual doses, air dose rate at the site boundary and impact of migrated radiocesium into groundwater. Firstly, we evaluated the additional annual dose for workers, on the assumption that typical workers coming in contact with the source after construction (Road: 1.2 mSv/y, Building: 1.3 mSv/y). Secondly, we evaluated the air dose rates by distance from road and building including recycling material, and investigated the distance for not exceeding 1 mSv/y (including additional dose rate by recycling and background dose rate of 0.6 mSv/y) at the site boundary (Road: 25 m, Building: 1 m). Thirdly, we evaluated the Cs migration in groundwater, and investigated the distance required for satisfying the operation target value ($$^{134}$$Cs: 1 Bq/L, $$^{137}$$Cs: 1 Bq/L) at the boundary (coastal line) (Road: 10 m, Building: 10 m).

Journal Articles

Comparison of the Fukushima radioactive mapping by two different aerial radiation monitoring systems

Kim, B.-J.*; Sasaki, Miyuki; Sanada, Yukihisa

Progress in Nuclear Science and Technology (Internet), 6, p.130 - 133, 2019/01

Journal Articles

Evaluation of ecological half-life of dose rate based on airborne radiation monitoring following the Fukushima Dai-ichi Nuclear Power Plant accident

Sanada, Yukihisa; Urabe, Yoshimi*; Sasaki, Miyuki; Ochi, Kotaro; Torii, Tatsuo

Journal of Environmental Radioactivity, 192, p.417 - 425, 2018/12

 Percentile:100(Environmental Sciences)

Journal Articles

Shielding

Maekawa, Fujio

Hamon, 28(4), p.208 - 211, 2018/11

Adequate shielding of neutrons and associated $$gamma$$-rays is of importance from viewpoints of the radiation safety of researchers and good experimental data taking by reducing the background. This article introduces basics of neutron shielding, physics and suitable materials for neutron and $$gamma$$-ray shielding, and an example of conceptual shielding design for the 1-MW spallation neutron source of J-PARC MLF.

Journal Articles

Behaviors of high-burnup LWR fuels with improved materials under design-basis accident conditions

Amaya, Masaki; Udagawa, Yutaka; Narukawa, Takafumi; Mihara, Takeshi; Taniguchi, Yoshinori

Proceedings of Annual Topical Meeting on Reactor Fuel Performance (TopFuel 2018) (Internet), 10 Pages, 2018/10

Journal Articles

A Study of methods to prevent piping and erosion in buffer materials intended for a vertical deposition hole at the Horonobe Underground Research Laboratory

Jo, Mayumi*; Ono, Makoto*; Nakayama, Masashi; Asano, Hidekazu*; Ishii, Tomoko*

Geological Society Special Publications, 482, 16 Pages, 2018/09

JAEA Reports

Annual report for FY2016 on the activities of Department of Decommissioning and Waste Management; April 1, 2016 - March 31, 2017

Department of Decommissioning and Waste Management

JAEA-Review 2018-008, 87 Pages, 2018/07

JAEA-Review-2018-008.pdf:2.67MB

This report describes the activities of Department of Decommissioning and Waste Management (DDWM) in Nuclear Science Research Institute (NSRI) in the period from April 1, 2016 to March 31, 2017. The report covers organization and missions of DDWM, outline and operation/maintenance of facilities which belong to DDWM, treatment and management of radioactive wastes, decommissioning activities, and related research and development activities which were conducted in DDWM.

Journal Articles

Development of experimental technology for simulated fuel-assembly heating to address core-material-relocation behavior during severe accident

Abe, Yuta; Yamashita, Takuya; Sato, Ikken; Nakagiri, Toshio; Ishimi, Akihiro; Nagae, Yuji

Proceedings of 26th International Conference on Nuclear Engineering (ICONE-26) (Internet), 9 Pages, 2018/07

Journal Articles

Evaluation of melting and solidification processes by laser irradiations using a computational science simulation code SPLICE

Muramatsu, Toshiharu

Dai-89-Kai Reza Kako Gakkai Koen Rombunshu, p.115 - 119, 2018/05

no abstracts in English

Journal Articles

Comparative study on prediction accuracy improvement methods with the use of integral experiments for neutronic characteristics of fast reactors

Yokoyama, Kenji; Kitada, Takanori*

Proceedings of 2018 International Congress on Advances in Nuclear Power Plants (ICAPP 2018) (CD-ROM), p.1221 - 1230, 2018/04

no abstracts in English

Journal Articles

Dimension-reduced cross-section adjustment method based on minimum variance unbiased estimation

Yokoyama, Kenji; Yamamoto, Akio*; Kitada, Takanori*

Journal of Nuclear Science and Technology, 55(3), p.319 - 334, 2018/03

 Times Cited Count:1 Percentile:38.14(Nuclear Science & Technology)

A new formulation of the cross-section adjustment methodology with the dimensionality reduction technique has been derived. This new formulation is proposed as the dimension reduced cross-section adjustment method (DRCA). Since the derivation of DRCA is based on the minimum variance unbiased estimation (MVUE), an assumption of normal distribution is not required. The result of DRCA depends on a user-defined matrix that determines the dimension reduced feature subspace. We have examine three variations of DRCA, namely DRCA1, DRCA2, and DRCA3. Mathematical investigation and numerical verification have revealed that DRCA2 is equivalent to the currently widely used cross-section adjustment method. Moreover, DRCA3 is found to be identical to the cross-section adjustment method based on MVUE, which has been proposed in the previous study.

Journal Articles

Recent statistical topics of nuclear material inventory verification

Kikuchi, Masahiro*; Suzuki, Mitsutoshi

Wiley StatsRef; Statistics Reference Online (Internet), 7 Pages, 2018/03

A near-real-time accountancy (NRTA) as a timely statistical test method for nuclear material inventory verification in international safeguards has a unique feature and development history, and it has been maintained and updated in large nuclear facilities in Japan. A recent discussion on approaches of measurement uncertainty may have impacted on the decision criteria of NRTA because its development origin dates back to the 1970's and derived from the conventional random and systematic error model. In this article, we will show the overview associated with this issue.

769 (Records 1-20 displayed on this page)